第五章编程题

 

1.

/*
**将标准输入复制到标准输出，将所有大写字母转换为小写字母。
*/

#include <stdio.h>
int main(void)
{
        int ch;
        while(ch = getchar() != EOF)
        {
            if (ch >= 'A' && ch <='Z')
                ch = ch + 'a' - 'A';
            putchar(ch);
        }


}

 

2.

/*从标准输入读取字符，并把它们写入到标准输出中，非字母字符按
**输入形式输出，字母字符加密，加密为字母表上距其13个位置的字母。
*/

#include <stdio.h>
int main(void)
{
        int ch;
        while(ch = getchar() != EOF)
        {
            if ((ch >= 'A' && ch <='M') ||
                (ch >= 'a' && ch <= 'm'))
                ch = ch + 13;
            else if ((ch >= 'N' && ch <= 'Z') ||
                     (ch >= 'n' && ch <= 'z'))
                     ch = ch - 13;
            putchar(ch);
        }


}

 

3

/*my code*/
unsigned int reverse_bits (unsigned int value)
{
    int a = 8 * sizeof (unsigned int);
    unsigned int i, j = 1;
    unsigned int new_value = 0;

    for (; a > 0 ; a--)             /* 一开始条件脑残地写成a <= 0*/
    {
        new_value <<= 1;
        new_value |= value & j;
        value >>= 1;
    }
    return new_value;
}
/*guide's answer*/
unsigned int reverse(unsigned int value)
{
    unsigned int answer;
    unsigned int i;

    answer = 0;

    for (i = 1; i != 0; i <<= 1)
    {
        answer <<= 1;
        if (value & 1)
            answer |= 1;
        value >>= 1;
    }
    return answer;
}

int main (void)
{
    unsigned int v = 0xfff;
    printf("%x\n%x\n", reverse_bits(v),reverse(v));

    return 0;
}

 

4.

/*
**guide中，求数组index以及位数bits用了函数，这样的话的确方便了，
**每次需要时调用即可，虽然这里不必这样，但当相同的表达式用到很多
**时就需要了，其中的思想应该学习。
*/

#include <limit.h>       /*这两个头文件???啥用呢*/
#include "bitarray.h"

void set_bit(char bit_array[], unsigned bit_number)
{
    unsigned int index, bits;

    index = bit_number / 8;
    bits  = bit_number % 8;

    bit_array[index] |= (1 << bit_number);
}


void clear_bit(char bit_array[], unsigned bit_number)
{
    unsigned int index, bits;

    index = bit_number / 8;
    bits  = bit_number % 8;

    bit_array[index] &= ~(1 << bit_number);
}
/*
**guide中直接调用上面两个函数，简单多了好不好！o(╯□╰)o
*/

void assign_bit(char bit_array[], unsigned bit_number, int value)
{
    unsigned int index, bits;

    index = bit_number / 8;
    bits  = bit_number % 8;

    if (value)
        bit_array[index] |= (1 << bit_number);
    else
        bit_array[index] &= ~(1 << bit_number);

}


int test_bit(char bit_array[], unsigned bit_number)
{
     unsigned int index, bits;

    index = bit_number / 8;
    bits  = bit_number % 8;

    bit_array[index] &= (1 << bit_number);

    if (bit_array[index])
        return 1;
    else
        return 0;
}

 

5.

int store_bit_filed
(int original_value,int value_to_store,
    unsigned starting_bit, unsigned ending_bit)
{
    /*step 1*/
    unsigned int c = starting_bit - ending_bit + 1;
    unsigned int mask = 1;
    unsigned int i;
    int new_value;

    for (i = 1; i < c; i++)
    {
        mask |= (mask << 1);
    }

    mask <<= ending_bit - 1;

    /*step 2*/
    original_value = original_value & (~mask);

    /*step 3此处课后的提示有误！！*/
    value_to_store <<= ending_bit -1;

    /*step 4*/
    value_to_store &= mask;
    return value_to_store;
    /*step 5*/
    new_value = value_to_store | original_value;

    //return new_value;


}

#include <stdio.h>
int main(void){

    printf("%x\n", store_bit_filed(0xffff, 0x123, 13, 9));


    return 0;
}